We propose to examine the regulation of hepatic heme synthesis at different stages of maturation by assaying enzymes of the heme biosynthetic pathways and the cytochrome P-450 system, which is involved in drug detoxification. Investigations will be directed toward an inquiry into the regulation of hemopexin synthesis by hormones and by heme and whether hemopexin synthesis in the fetus is comparable to that of adult rats. BIBLIOGRAPHIC REFERENCES: Effect of hemoglobin and hematin on plasma clearance of hemopexin, photoinactivated hemopexin and albumin. H. H. Liem, J. I. Spector, T. P. Conway, W. T. Morgan, and U. Muller-Eberhard, Proc. Soc. Exp. Biol. Med. 148:519-522, 1975. Porphyrin binding proteins in serum. U. Muller-Eberhard and W. T. Morgan, Ann. N. Y. Acad. Sci. 244:624-650, 1975.